Pigment



lPatented Dec. 13, 1938 PATENT OFFICE PIGMENT Ekbert Lederle,Ludwigshai'en, Max Gi'mther,

Mannheim, and Rudolf Brill, Heidelberg, Germany No Drawing. ApplicationMay 15, 1937, Serial No. 142,928. In Geny March 14, 1934 10 Claims.

This application is a continuation in part of our copending application,Serial No. 11,164, filed March 14, 1935, for the manufacture of whitepigments comprising zinc titanates.

This invention as compared to that described together by means of aflux, a titanium-oxygen.

compound and a metallic oxide. Neither of these methods has producedtitanate pigments which satisfactorily meet the requirements of modernpigment standards.

The first of the above noted prior art methods tends to yield productsin which a considerable portion of the starting ingredients remainsuncombined. If the temperature is unduly raised or the heating undulyprolonged with a view to obtaining a more complete combination, theproducts become hard, coarse and gritty and badly discolored. The secondof the above noted prior art methods, while it tends toward a morecomplete combination, yields products which can never be pulverized to asufficient degree of fineness, uniformity and soft, smooth texture whichare required of a modern pigment. Although, in respect to chemicalcomposition, prior art preparations may have represented titanates ofvarious metals, such products, without exception, have provenunadaptable for use as pigments.

By means of the present invention as herein set forth metallic titanatesmay be.prepared which possess a fineness, uniformity of particle size,clarity of color, smooth and soft texture and other pigment propertiesrendering them eminently suited for use as pigments.

Thus an object of our invention is an improved method for preparingtitanate pigments. Another object of our invention is a method forcontrolling particle size and texture of titanate pigments. These andother objects of our invention will become apparent from the followingdescription thereof.

In our aforementioned application, Serial No. 11,164, we have disclosedcertain improvements in the preparation of zinc titanate pigments. Theseimprovements, we have found, are equally adaptable to the manufacture ofmetallic titanates generally.

Briefly described, our invention consists of three features whichconsidered jointly, constitute a complete process for preparation ofpigmentary metallic titanates. However, each individual feature may beemployed in connection with a method for preparing metallic titanatesnot embodying the other herein described features with a resultingimprovement in the pigment properties of the metallic titanatesobtained.

The first feature of the present invention may be described as themutual precipitation of ingredients which are contained in the startingmixture, for example, reactive metallic compounds and reactive titaniumcompounds.

The second feature of the present" invention is a calcination of thestarting mixture throughout a range of increasing temperature such as isobtainable, for example, in a two-step calcination.

The third feature of the present invention is a treatment of thestarting mixture or the calcined product at elevated temperatures andpressures in the presence of water which may or may not contain certainaddition agents.

We have found that when one or all ingredients of the starting mixtureof reactive metallic compounds and reactive titanium compounds isprepared by mutual precipitation there is obtained an extremely uniformand intimate mixture of the ingredients having a very fine particlesize. Such a uniform mixture of fine particle size is highly desirablesince it permits this reaction to go substantially to completion withoutexcessive heating at elevated temperatures.

Furthermore, the products resulting from such I mixtures are moreuniform in particle size than those obtained by prior art methods.

Thus, according to this feature of our invention, one of the ingredientsin finely-divided form may be suspended in an aqueous solution of a saltof the other ingredient and both ingredients precipitated by causing thesoluble ingredient to precipitate as a water-insoluble cornpound. Forexample, hydrous titanium oxide or titanium dioxide may be suspended inan aqueous solution of a salt of a metal capable of forming a titanate.The metal may then be precipitated from solution upon the addition of areagent capable of forming a water-insoluble reactive metal compound.

By reactive metal compound we mean to include the compounds of metals,such as the oxides, hydroxides, carbonates, and other compounds whichwill decompose at the calcination temperatures employed to yield theoxide, and which will react with titanium at elevated temperatures toform titanates. An example of such procedure is to suspend titaniumdioxide in a solution of zinc sulfate or chloride and to add thereto asolution of sodium carbonate which will precipitate a zinc carbonate andtitanium dioxide in an intimate and uniform mixture of fine particlesize.

By reactive titanium compounds we mean to include titanium dioxide andany titanium compounds which will decompose at the calcinationtemperatures employed to yield titanium dioxide.

On the other hand, according to this feature of our invention, it ispossible to suspend finelydivided reactive metal compounds in solutionsof titanium, such as a titanium sulfate solution and to precipitatetherefrom the titanium, either hydrolytically by heating the mixture orby the addition of an alkaline neutralizing agent to precipitateortho-titanic acid.

Alternatively, according to this same feature of our invention, it ispossible to mix together aqueous solutions of salts of the ingredientswhich are to make up the starting mixture and to precipitate both thereactive metal compounds and the reactive titanium compound from themixed solution. For example, we may mix together a solution of nickelsulfate and a solution of titanium sulfate and add thereto a solution ofsodium hydroxide, thus precipitating nickel hydroxide and ortho-titanicacid.

Our invention is not limited to any particular metal but is applicableto the preparation of titanates of any metal which is capable of beingprecipitated as reactive metal compound from an aqueous solution of awater-soluble salt of the said metal. Single or mixed titanates ofaluminum, barium, cadmium, calcium, cobalt, copper, iron, lead,manganese, magnesium, nickel, strontium and zinc, may be prepared fromthe starting mixtures obtained by the mutual precipitation metals justdescribed. It will be understood, of course, that the metallic compound,

if precipitated, must be reactive, that is to say, it must be in a formcapable of yielding oxide at the calcination temperatures employed inthe formation of the titanates. Such reactive forms will include, ofcourse, the oxides and hydroxides of the metals above enumerated; itwill include also the hydrocarbonates, hydrosulfldes and many of thecarbonates and sulfides as well.

We further found that when a starting mixture of reactive metalcompounds and reactive titanium compounds is calcined throughout arangeof increasing temperature, a more complete combination is obtainedwithout imparting to the product the undesirable hardness anddiscoloration which results at the elevated temperature necessary toobtain substantially complete combination as employed by the prior art.

Such a calcination may suitably be carried out as a two-step methodwherein the starting mixture is first calcined at a comparatively lowtemperature and then heated at a comparatively higher temperatura' Bysuch procedure the titanate is formed substantially completely at thelow temperature.

"develop the crystallinity of the product and to The high temperatureserves to increase the particle size as desired. For example.the'titanates of the above listed metals may be formed by heating thedesired starting mixture at a temperature between about 500 and about800 0., after which the temperature may be raised up to 1100 C. untilthe proper particle size is obtained.

As stated in our copending Serial No. 11,164, we found that an increasein particle size improves the pigment properties and that this increasein particle size can be followed by means of the X-ray. When the producthas attained a particle size of about 10- cm. sharp interference linesbegin to appear on the X-ray plate. These lines increase in sharpness asthe particle size increases with corresponding improvement in thepigment properties, particularly weatherresistance and freedom fromchalking. Consequently, according to this feature of our invention thetitanate formation may be carried to substantial completion in one stepand then the particle size controlled in the second step. This was notpossible in prior art methods because at the elevated temperaturesrequired by the prior art to substantially complete the formation of thetitanate, titanate formation and growth of particle size were going onside by side during the heating. As a result prior art products variedgreatly in particle size, whereas the products of the present inventionare uniform and even textured.

It will be understood, of course, that it is possible, according to thisfeature of our invention, to prepare the titanate in a reaction vessel,such as a rotary calciner, wherein the starting mixture will enter thelow temperature region and progressively move through the calciner at arate of speed suiiicient to hold the mixture within the low temperaturerange until titanate formation is substantially complete before passinginto the higher temperature regions. Accordingly, this feature of ourinvention is not limited to a. two.- step calcination, per se, but isdirected to a heat treatment by means of which the titanate formation issubstantially completed before any appreciable growth of particle sizeoccurs.

We have further discovered that the texture and. the softness of thetitanate pigments which may be prepared according to the presentinvention may be improved by subjecting the calcined product or thestarting mixture to apressure treatment at elevated temperatures in thepresence of H20. Thus, a metallic titanate may be moistened with waterpreferably to form a slurry and heated in an autoclave to temperaturesbetween 110 and about 500 for about 1 to about 4 hours. The resultingtitanates will possess improved covering power and low oil absorption;it will also possess a smooth and soft texture. Although it ispreferable to carry out this treatment on the calcined titanate, similaradvantages may be obtained by subjecting the starting mixture to apressure treatment as described. Such a treatment is particularly usefulwhen starting mixtures are prepared by methods other than those of thepresent invention.

,The effect of the pressure treatment may be enhanced by the addition ofvery small amounts the advantage accruing from the pressure treatment.The amounts of such materials may vary between 0.01% and 1.0% based onthe Weight of the pigment to be treated.

Having thus described our invention the following examples are given forillustrative purposes only, but it will be understood no limitations asto temperatures, proportions, time of heating, etc., are to be deducedtherefrom.

Example 1.-Illustrating (a) the precipitation of the reactive metalcompound in the presence of the TiOz; (b) two-step calcination; (c)pressure treatment after calcination One kilogram of finely-dividedcalcined titanium hydroxide, TlOz is suspended in about 10 liters of acalium chloride solution containing about 1260 grams CaClz in solution(equivalent to 1 kilogram CaCl2). A sufficient amount of a 20% solutionof sodium carbonate is added to precipitate the calcium as CaCOa. Thetitanium dioxide, of course, settles out of suspension with theprecipitating CaCO3. The resulting finelydivided and uniform mixture isheated to about 750 C. for about 2 hours, the temperature is then raisedto about 950 C. for about 1 hour. The product after cooling ispulverized and then mixed with water to form a free slurry, after whichit is heated for about 2 hours in a rotating autoclave for about 2 hoursat 200 C.

The resulting calcium metatitanate is a substantially pure whitepigment. It will possess a smooth, soft texture, low oil absorption anda uniform particle size.

Example 2.Illustrating the pressure treatment prior to calcination usingaddition agents In a variation of Example No. l, the starting mixture oftitanium dioxide and precipitated calcium compound is subjected to apressure treatment in the presence of water containing a trace ofhydrochloric acid for 3 hours at 200 C., prior to calcination.

Example 3.--Illustrating (a) the precipitation of orthotitanic acid inthe presence of reactive metal compound; (b) use of a graduallyincreasing temperature One kilogram of finely-divided zinc oxide issuspended in five kilograms of a titanium sulfate solution containingabout 500 grams T102 in solution. The TiOz is precipitated asorthotitanic acid by adding an aqueous solution of sodium hydroxide. Theuniform mixture of zinc oxide and orthotitanic acid is washed and may ormay determined by withdrawing a sample and testing.

for free ZnO by means of an ammoniacal ammonium salt solution afterwhich it passes into a zone of higher temperature, not exceeding 950 C.

until a particle size of about 10- cm. is obtained as determined byX-ray analysis.

The resulting zinc orthotitanate is, after pulverizing, a pure whitepigment, uniform in particle size, smooth in texture and substantiallfree from uncombined H02 and ZnO.

Example 4.Illustrating the precipitation of both titanium compound andthe reactive metal compound Four hundred grams of magnesium oxide, MgO.is thoroughly mixed with hydrous titanium oxide containing about 900grams of T102, from which impurities, including the sulfate radical havebeen removed. The resulting mixture is dissolved in sulfuric acid toobtain a solution of magnesium and titanium sulfates. This solution isthen treated with caustic alkali solution until a mixed precipitate ofthe titanium and magnesium constituents results. This intimate anduniform mixture will serve as an excellent starting mixture for thepreparation of magnesium metatitanate MgTiOs of pigment quality.

Example 5.-Illustrating the two-step calcination One mol. offinely-divided litharge, PbO, is intimately mixed with hydrolyticallyprecipitated hydrous titanium oxide containing one mol. TiOz and someadsorbed or combined S04. This intimate mixture is first heated forabout 2 hours at 600 C. for about 2 hours during which the titanateformation is substantially complete and volatile impurities are drivenoff. The temperature is then raised to about 800 C. for about 4 hours todevelop crystallinity and growth of particle size.

The resulting lead titanate, after calcination, is slightly yellow incolor. It is uniform in particle size, has a smooth, even texture and isexcellently adapted for use as a pigment.

It will be understood, of course, that it is impossible to give specificexamples of all metallic titanates, whether they be simple titanates ofa single metal or mixed titanates of two or more metals. It will beappreciated that our invention, as herein described and illustrated, maybe subjected to various modifications and variations Within the skill ofthe operator without departing from the scope of the invention. Forexample, fluxes, such as alkaline metal sulfates or chlorides, borates,tungstates, and vanadates, and the like, may be employed to cut down thetime of reaction, care being taken that the use of such fluxes isrestricted to an amount which will not bring about a fusion of thereaction mixture.

Among the many simple titanates which may be prepared according to thepresent invention, are the following: white zinc titanate, blue-greeniron titanate, yellow nickel titanate, green cobalt titanate, whitecalcium titanate, white magnesium titanate, blue-green or red manganesetitanate, light yellow lead titanate, yellow to white barium titanate,white strontium titanate and white cadmium titanate. Many beautifulcolored titanates may be prepared according to our invention whichcontain two or more metals in addition to the titanate radical, andwhich are regarded as mixed titanates. For example, a beautiful bluepigment may be prepared by a calcination of a starting mixture, areactive cobalt compound, a reactive aluminum compound and a reactivetitanium compound.

The products prepared according to the present invention are usefulparticularly in surface coating compositions but are also generallyuseful wherever high quality pigments are desired. Furthermore, they maybe mixed in the wellknown manner with the usual extenders to formcomposite titanate pigments.

The foregoing description has been given for clearness of understandingand no undue limitations should be deduced therefrom, but the appendedclaims should be considered as broadly as possible in the light of theprior art.

We claim: 1

1. Process for the preparation of pigmentary metallic titanates whichcomprises preparing a uniform and intimate mixture of reactive metalcompounds with reactive titanium compounds by mutual precipitation fromaqueous media, heating the mixture so obtained at a gradually increasingtemperature within the range of about 500 C. to about 1100 C., thetemperature being maintained first within the range of about 500 C. toabout 800 C. until the formation of titanate is substantially completeand being thereafter maintained within the range of about 800 C. toabout 1100 C. until the product exhibits sharp interference lines on anX-ray photograph mixing the calcined product with water and then heatingthe mixture under pressure at an elevated temperature.

2. Process for the preparation of pigmentary metallic titanates whichcomprises preparing a uniform and intimate mixture of reactive metalcompounds and reactive titanium compounds by mutual precipitation fromaqueous media, and heating the mixture so obtained at a temperaturewithin the range of about 500 C. to about 800 C. until titanateformation is substantially complete and then heating the titanate at ahigher temperature within the range of about 800 C. to about 1100 C.until the heated products exhibit sharp interference lines on an X-rayphotograph.

3. In a method for preparing pigmentary metallic titanates whichincludes the thermal combination of reactive metal compounds withreactive titanium compounds, the step which consists in heating anintimate and uniform mixture of reactive metal compounds with reactivetitanium compounds at a gradually increasing temperature within therange of about 500 C. to about 1100 C., the temperature being maintainedfirst within the range of about 500 C. to about 800 C. until theformation of titanate is substantially complete and being thereaftermaintained within the range of about 800 C.

to about 1100 C. until the product exhibits sharp interference lines onan X-ray photograph.

'4. In a method of preparing pigmentary metallic titanates whichincludes the thermal combination of reactive metal compounds withreactive titanium compounds, the steps which consist in heating anintimate and uniform mixture of reactive metal compounds with reactivetitanium compounds within the range from about 500 C. to about 1100 C.,the temperature being maintained in a first stage at between about 500C. and about 800 C. until titanate formation is substantially completeand being thereafter maintained at a higher temperature than in thefirst stage not exceeding about 1100 C. until the heated productexhibits sharp interference lines on an X-ray photograph.

5. In a method for preparing pigmentary metallic titanates whichincludes the thermal combination of reactive metal compounds withreactive titanium compounds, the step which conareaaec sists in heatingan intimate and uniform mixture of reactive metal compounds withreactive titanium compounds at a gradually increasing temperature withinthe range of about 500 C. to about 1100 C., the temperature beingmaintained first within the range of about 500 C. to about 800 C. untilthe formation of titanate is substantially complete and being thereaftermaintainedwithin the range of about 800 C. to about 1100 C. until theproduct exhibits sharp interference lines on an X-ray photograph in thepresence of a small amount of a flux.

6. In a method for preparing metallic titanates which consists inheating a starting mixture of reactive metal compounds and reactivetitanium compounds, the step which consists in subjecting the startingmixture prior to heating to a pressure treatment at an elevatedtemperature in the presence of H20.

7. In a method for preparing metallic titanates which consists invheating a starting mixture of reactive metal compounds and reactivetitanium compounds, the step which consists in subjecting the titanateobtained after heating to a pressure treatment at an elevatedtemperature in the presence of H20.

8. In a method for preparing metallic titanates which consists inheating a starting mixture of reactive metal compounds and reactivetitanium compounds, the step which consists in subjecting the startingmixture prior to heating to a pressure treatment at an elevatedtemperature in the presence of H20 containing a small amount of an addedsoluble substance selected from the group consisting of acids, bases andsalts.

9. In a method for preparing metallic titanates which consists inheating a starting mixture of reactive metal compounds and reactivetitanium compounds, the step which consists in subjecting the titanateobtained after heating to a pressure treatment at an elevatedtemperature in the presence of H20 containing a small amount of an addedsoluble substance selected from the group consisting of acids, bases andsalts.

10. In a method of preparing pigmentary magnesium titanate whichincludes the thermal combination of a reactive magnesium compound with areactive titanium compound the step which consists in first heating anintimate and uniform mixture of a reactive magnesium compound with areactive titanium compound at a temperature within the range of about500 C. to about 800 C. until formation of magnesium titanate issubstantially complete and then heating the magnesium titanate at ahigher temperature within the range of about 800 to about 1100 C. untilthe magnesium titanate exhibits sharp interference lines on an X-rayphotograph.

, EKBERT LEDERLE.

'. MAX GiiNTHER. RUDOLF BRILL.

